Method for allocating secondary synchronization codes to a base station of a mobile telecommunication system

ABSTRACT

According to the invention, the method comprises the steps of calculating and evaluating the auto-correlation functions and/or cross-correlation functions of N possible secondary synchronization codes (SSC) and the primary synchronization code (PSC) and choosing the M secondary synchronization codes (SSC) amongst said N possible secondary synchronization codes (SSC) so that said the M chosen secondary synchronization codes (SSC) have at least one of the statistical properties of their auto-correlation function and cross-correlation function that is best in term of detection, and allocating a sub-set of said M secondary synchronization codes (SSC) comprising K secondary synchronization codes (SSC) to said base station.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.10/030,421, filed May 22, 2002, now U.S. Pat. No. 6,728,297 the entirecontents of which are hereby incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to a method for allocating secondarysynchronization codes to a base station of a mobile telecommunicationsystem.

BACKGROUND ART

The present invention relates to a mobile telecommunication systemcomprising a number of base stations which can communicate with mobilestations. A communication from a mobile station to a base station isdone by means of an up-link UL and the communication from a base stationto a mobile station is done by means of a down-link DL.

The present invention relates also to a telecommunication systemswherein different user signals are separated both in time domain and incode domain. An example of such a system is the so called UMTS TDDsystem (Universal Mobile Telecommunication Systems—Time Division Duplex)or W-CDMA TDD system (Wideband Code Division Multiple Access—TimeDivision Duplex) in which the time domain is represented by theTDD-system component and the code domain by W-CDMA-system component.

More particularly, in time-domain, transmission is for example organizedbased on radio frames constituted of a number (for example 15) oftimeslots. The same frequency is used for both the up-link (MobileStation to Base Station) and the down-link (Base Station to MobileStation). Furthermore, a time-separation is used to differentiate thedown-link and the up-link such that a subset of all the availabletimeslots per frame is exclusively allocated for down-link transmissionand the remaining ones for up-link transmission. In a frame, at leastone timeslot is always allocated for each down-link and up-link.

In such a system, different user's signals can be transmitted inseparate timeslots, e.g. N different down-link timeslots are allocatedto N different down-link user signals. This is the time-division aspectof the system. Furthermore, several users signals can also betransmitted within one timeslot by using different spreading codes. Thisis the code-division aspect of the system. Note that each user isallocated a different spreading code and that each user bit is spread tothe chip-rate as function of the employed spreading factor.

In such a system, the network allocates to each cell covered by the basestations different cell parameters which enable any mobile stationattempting to establish connection to said base station to read cellbroadcast information needed to communicate therewith. These cellparameters indicate for example a midamble number and a scrambling code.The midamble is a complex- or real-valued chip sequence and is used by areceiver (a mobile station in the downlink) for channel estimation whichis needed for the retrieval of the user's signals. The scrambling codeis used by the transmitter (a base station in the downlink) to scramblethe user's signals in order to average the interference caused to user'swho are sending or receiving in neighboring cells.

When a mobile station gets switched on, it must first find out chip,slot and frame timing of at least one cell covering the area in which itis and then find out which midamble and scrambling code are used beforeit can demodulate and read the cell broadcast information. Afterwards, atracking mechanism ensures that especially chip timing is not lost, oncethe mobile station is “synchronized” to the cell.

Each base station, for each cell, transmits the cell broadcastinformation on a channel which is generally the so-called Primary CommonControl Physical Channel (P-CCPCH). It can also be the Secondary CommonPhysical Channel (S-CCPCH) when it is pointed to by the Primary CommonControl Physical Channel P-CCPCH.

Note that a Primary Common Control Physical Channel P-CCPCH in theW-CDMA TDD system generally uses a fixed and pre-allocated spreadingcode with fixed spreading factor, e.g. its spreading code is the same inall cells of the W-CDMA TDD system and therefore always knownbefore-hand by the mobile station.

A physical synchronization channel (PSCH) is also transmittedsimultaneously in those timeslots in the downlink where a Primary CommonPhysical Channel P-CCPCH is transmitted for the purpose ofsynchronization to the Primary Common Control Physical Channel(P-CCPCH). The Physical Synchronization Channel essentially consists oftwo special signals: the primary synchronization code PSC and a set of Ksecondary synchronization codes SSC. The number K of secondarysynchronization codes SSC is generally 3. A Primary Common PhysicalChannel P-CCPCH is never allocated to a particular timeslot when thereis no Primary Synchronization Channel PSCH simultaneously present. Ifthe mobile station finds out in which timeslots the PrimarySynchronization Channel PSCH is sent, it knows that the Primary CommonPhysical Channel P-CCPCH is also in this timeslot.

Each of the K in parallel transmitted secondary synchronization code SSCspreads a symbol having a number n of states, i.e. a modulatedQuadrature Phase Shift Keying (QPSK) symbol, which gives a total ofn^(K) QPSK codewords.

On one hand, the combination of the code sets, e g. different tripletsto spread the QPSK-symbols and, on the other hand, the modulation ofthese QPSK-symbols are used for indicating:

-   -   A Code Group for which are defined univocally one or several        cell parameters, e g. one or several scrambling codes together        with one or several basic short or long midamble codes,    -   The position of the Primary Synchronization Channel PSCH within        a double-frame period, and    -   The position of the current Primary Synchronization Channel PSCH        timeslot within one frame.

Finally, at power-on, a mobile station first searches by performing acorrelating process for the presence of the Primary Synchronization CodePSC transmitted on the Primary Synchronization Channel PSCH by the basestation of the cell under the coverage of which it is and uses the foundtime positions for correlating with all possible secondarysynchronization codes SSC, generally 16. By performing a coherentdetection, e.g. using the Primary Synchronization Code PSC as a phasereference for the secondary synchronization codes SSC, it can alsodetect the QPSK-symbols spread by the K detected secondarysynchronization codes SSC. From this information it can derive the timeposition of the Primary Synchronization Channel PSCH slot within theframes period as well as the Code Group to which the base stationbelongs. In a last step, the mobile station can demodulate a burst onthe Primary Common Control Physical Channel P-CCPCH by trying all stillpossible of Scrambling Codes and Basic Midamble Codes which arecontained in the found Cod Group.

Each secondary synchronization code SSC is a different binary-valuedchip sequence which is referenced by a particular index. For example,when 16 secondary synchronization codes SSC are possible in the mobilecommunication system, each secondary synchronization code SSC isindicated by one of the following values:

SSC₀, SSC₁, SSC₂, . . . , SSC₁₅.

For example, each of the secondary synchronization code SSC is formedaccording to the rules defined in the Technical Specifications 3GPP TSGRAN TS25.213 v320 “Spreading and Modulation (FDD)”, section 5.2.3.1 page21ff. and 3GPP TSG RAN TS25.223 v320 “Spreading and Modulation (TDD)”,section 7.1 page 10ff.

Not all of the possible and available secondary synchronization codesSSC are used simultaneously in a cell for the synchronization purposesabove described Currently, for making the choice of each set of Ksecondary synchronization codes SSC allocated to a cell, the networktakes out of the N possible ones, the first K secondary synchronizationcodes SSC, then the second K secondary synchronization codes SSC, etc. Mout of N are chosen, the last N−M being unused. For the W-CDMA TDD,system, wherein K is 3 and N is 16, for simplicity reasons, thefollowing 4 code groups (e.g. triplets of SSC) are chosen by the networkand allocated to the specific cells:

Code group 1: SSC₀, SSC₁, SSC₂

Code group 2: SSC₃, SSC₄, SSC₅.

Code group 3: SSC₆, SSC₇, SSC₈.

Code group 4: SSC₉, SSC₁₀, SSC₁₁.

Thus, only M=K*L secondary synchronization codes SSC out of N possibleand available ones are used for synchronization purposes

The performance of the synchronization process above described is verysensible to the errors than can occur during transmission or during thecorrelation processes performed for the retrievals of the primarysynchronization code PSC and of the secondary synchronization codes SSC.

DISCLOSURE OF INVENTION

It is an object of the invention to provide a method for allocatingsecondary synchronization codes SSC to a base station of a mobiletelecommunication system in order to improve the performance of thesynchronization process.

Generally speaking, in a system concerned with the invention, each basestation continuously transmits a primary synchronization code PSC and aset of K secondary synchronization codes SSC respectively allocated tothe cell covered by said base station so that any mobile station, whengetting switched on, can, on basis of the primary synchronization codePSC and the set of secondary synchronization codes SSC received fromsaid base stations synchronize with at least one base station in orderto read cell parameters. Furthermore, only a predetermined and fixednumber M of secondary synchronization codes SSC amongst all the Npossible and available secondary synchronization codes SSC are used.

According to a feature of the invention, the method comprises the stepsof calculating and evaluating the auto-correlation functions and/orcross-correlation functions of N possible secondary synchronizationcodes SSC and the primary synchronization code PSC and of selecting theM secondary synchronization codes SSC amongst said N possible secondarysynchronization codes SSC so that said M chosen secondarysynchronization codes SSC have at least one of the statisticalproperties of their auto-correlation function and cross-correlationfunction that is best in term of detection, and allocating a sub-set ofsaid M secondary synchronization codes SSC comprising K secondarysynchronization codes SSC to said base station.

Note that the auto- and cross-correlation functions can either beevaluated over the entire range, but also only over a limited window.That means that a subset of all possible auto- or cross-correlationvalues can be taken for evaluation.

It has been found that the statistical auto-correlation functionproperties of these synchronization codes are of primary importance forCell Search performance as they directly impact the probability of falseor erroneous detection.

Also, whenever a primary synchronization code PSC and one or moresecondary synchronization codes SSC are sent in parallel, theauto-correlation function of the primary synchronization code PSC aswell as the auto-correlation function of the secondary synchronizationcodes SSC suffer from undesired cross-correlation functions caused bythe simultaneous presence of another synchronization code.

According another feature of the present invention, the selection stepis based upon the evaluation of any statistical property or combinationof it of the following correlation functions:

(1) auto-correlation function of each secondary synchronization code SSC

(2) cross-correlation functions of each secondary synchronization codeSSC with the primary synchronization code PSC,

(3) cross-correlation functions of every secondary synchronization codesSSC with any other secondary synchronization code SSC.

These above criteria can be applied separately or combined

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 and 2 respectively show the auto-correlation functions of thesecondary synchronization code SSC₃ and the secondary synchronizationcode SSC₇ and their respective cross-correlation functions with theprimary synchronization code PSC,

FIG. 3 shows the difference between the auto-correlation functions ofthe secondary synchronization code SSC₃ and the secondarysynchronization code SSC₇ that can also be observed for the statisticalproperties of their pair-wise mutual cross-correlation functions withall other secondary synchronization codes SSC (displayed sequentialorder in FIG. 3), and

FIG. 4 shows tables wherein are given statistical properties of theauto-correlation functions and the cross-correlation functions ofstate-of-the-art synchronization codes available in a W-CDMA TDD system.

BEST MODE FOR CARRYING OUT THE INVENTION

FIGS. 1 and 2 respectively show the auto-correlation functions of thesecondary synchronization code SSC₃ and the secondary synchronizationcode SSC₇ and their respective cross-correlation functions with theprimary synchronization code PSC The synchronization codes used forFIGS. 1 and 2 are current state-of-the-art synchronization codesavailable in a W-CDMA TDD system.

From these examples, it becomes clear that the auto-correlationfunctions of the secondary synchronization codes SSC₃ and SSC₇ are quitedifferent, the auto-correlation function of the secondarysynchronization code SSC₃ being better in term of detection Furthermore,the cross-correlation function of the primary synchronisation code PSCand the secondary synchronization code SSC₃ is worse in term ofdetection than the cross-correlation of the primary synchronization codePSC and the secondary synchronization code SSC₇

FIG. 3 shows the difference between the secondary synchronization codesSSC₃ and SSC₇ that can also be observed for the statistical propertiesof their pair-wise mutual cross-correlation functions with all othersecondary synchronization codes SSC (displayed sequential order in FIG.3).

According to one aspect of the invention, said statistical propertiesare one or several properties of the total energy contained by saidauto-correlation functions and/or cross-correlation functions.

Statistically, the auto-correlation function can be characterized by itsmaximum auto-correlation side-lobe value (MAS-value). It can also becharacterized by more than one values of its maximum side-lobes It canstill be characterized by the root of the mean of the total energycontained in all side-lobe peaks (RMS) value.

Similar to the auto-correlation function, the cross-correlation functioncan be characterized by its maximum cross-correlation peak (MCP) value,by more than one values of its maximum peaks or by the root of the meanof the energy contained by all the cross-correlation peaks (RMS) value.

Generally speaking, the detection performance of a particularsynchronization code will improve, when the maximum auto-correlationside-lobe value (MAS) and the root of the mean of the energy (RMS) valueof its auto-correlation function and all maximum cross-correlation peakvalues (MCP) and the root of the mean of the energy peaks (RMS) valuesof its cross-correlation with all other possible synchronization codesdecrease. Choosing synchronization codes with good auto-correlation andgood cross-correlation properties improves the overall Cell Searchperformance and as such increases the performance of the synchronizationprocedure and reduces mobile station processing load and its batterylife.

According another feature of the invention, the method comprises thestep of choosing the best L groups composed of K secondarysynchronization codes SSC, such that M=K*L, within all possiblecombinations out of N possible and available secondary synchronizationcodes SSC within the sub-set of the M used secondary synchronizationcodes SSC.

Note that in any case, a selection and therefore optimization ofcorrelation properties for the sub-set of employed synchronization codesis always possible, as long as M<N.

According another feature of the invention, the selection step of the Msecondary synchronization codes SSC comprises the steps of discardingthe N−M secondary synchronization codes SSC that have at least one ofthe statistical properties of their auto-correlation function andcross-correlation function which are worst in term of detection and ofkeeping the M remaining secondary synchronization codes SSC.

Table 1, table 2 and table 3 of FIG. 4 summarize some of the statisticalproperties for the auto-correlation function and all cross-correlationfunctions of the current state-of-the-art synchronization codes whichare available in the W-CDMA FDD and TDD system and that are described inthe Technical Specifications 3GPP TSG RAN TS25.213 v320 “Spreading andModulation (FDD)”, section 5.2.3.1 page 21ff and 3GPP TSG RAN TS25.223v320 “Spreading and Modulation (TDD)”, section 7.1 page 10ff.

Referring to Table 1, the selection of the M=12 secondarysynchronization codes SSC gives the following result when discarding theN−M=4 secondary synchronization codes SSC having the worst value of theoff-peak maximum auto-correlation side-lobe values (MAS) in theirauto-correlation function and keeping the remaining: SSC₀, SSC₁, SSC₂,SSC₃, SSC₆, SSC₇, SSC₈, SSC₉, SSC₁₂, SSC₁₃, SSC₁₄, SSC₁₅.

When discarding the N−M=4 secondary synchronization codes SSC having theworst value of the root of the mean of the energy peaks (RMS) value intheir auto-correlation function and keeping the remaining, the resultis: SSC₀, SSC₁, SSC₂, SSC₃, SSC₆, SSC₇, SSC₈, SSC₉, SSC₁₂, SSC₁₃, SSC₁₄,SSC₁₅.

When discarding the N−M=4 secondary synchronization codes SSC having theworst maximum cross-correlation peak value (MCP) in theircross-correlation function with the primary synchronization code PSC andkeeping the remaining, the result is: SSC₀, SSC₁, SSC₃, SSC₄, SSC₅,SSC₆, SSC₈, SSC₁₀, SSC₁₂, SSC₁₃, SSC₁₄, SSC₁₅.

When discarding the N−M=4 secondary synchronization codes SSC having theworst value of the root of the mean of the energy peaks (RMS) in theircross-correlation function with the primary synchronization code PSC andkeeping the remaining, the result is SSC₀, SSC₁, SSC₄, SSC₅, SSC₆, SSC₈,SSC₁₀, SSC₁₁, SSC₁₂, SSC₁₃, SSC₁₄, SSC₁₅

When discarding the N−M=4 secondary synchronization codes SSC having theworst maximum cross-correlation peak value (MCP) in theircross-correlation functions with the all other secondary synchronizationcodes SSC and keeping the remaining, the result is SSC₀, SSC₁, SSC₂,SSC₄, SSC₈, SSC₉, SSC₁₀, SSC₁₁, SSC₁₂, SSC₁₃, SSC₁₄, SSC₁₅.

When discarding the N−M=4 secondary synchronization codes SSC having theworst value of the root of the mean of the energy peaks (RMS) in theircross-correlation function with all other secondary synchronizationcodes SSC and keeping the remaining, the result is SSC₀, SSC₂, SSC₄,SSC₅, SSC₆, SSC₇, SSC₈, SSC₁₀, SSC₁₁, SSC₁₂, SSC₁₃, SSC₁₄.

According to another feature of the invention, the selection step of theM secondary synchronization codes SSC comprises the steps of selectingthe best L code groups in term of detection, each group being composedof K distinct secondary synchronization codes SSC, such that M=K*L, outof all the N possible and available secondary synchronization codes SSCof the system.

For example, all the possible combinations of L code groups, composedeach of K distinct secondary synchronization codes SSC, such thanM=L*K<N, are considered and the statistical properties or theauto-correlation function of the secondary synchronization codes SSC ofeach code group, the statistical properties of the cross-correlationfunctions with all other secondary synchronization codes SSC in the sameand other code groups and with the primary synchronization code PSC ofeach is determined. Then, these properties are evaluated and comparedwith those of the known code groups and the best combination of L(L=M:K) code groups are selected.

Suppose the number N of possible secondary synchronization codes SSC ofthe system is 16 and that they are those shown in Table 1.

The selection of L=4 sets of secondary synchronization codes SSC,composed each of K=3 distinct secondary synchronization codes SSCamongst the N=16 possible and available secondary synchronization codesSSC of the system according the embodiment of the selection step givenbelow gives the following result: {SSC₁, SSC₂, SSC₃; SSC₁₂, SSC₁₃,SSC₁₄; SSC₀, SSC₆, SSC₁₅; SSC₅, SSC₈, SSC₁₁}.

According to another feature of the invention, the selection step of theM secondary synchronization codes SSC comprises the steps of selectingthe best code groups in term of detection, each group being composed ofK distinct secondary synchronization codes SSC out of M pre-selected,for example according to a preceding selection step of the method of theinvention, secondary synchronization codes SSC.

As before, all the possible combinations of L code groups, composed eachof K distinct secondary synchronization codes SSC, such that M=L*K<N,which can be formed from the M pre-selected secondary synchronizationcodes SSC are considered and the statistical properties of theauto-correlation function of the secondary synchronization codes SSC ofeach code groups, the statistical properties of the cross-correlationfunctions with all other secondary synchronization codes SSC in the sameand other code groups and with the primary synchronization code PSC ofeach is determined. Then, these properties are evaluated and comparedwith those of the known code groups and the best combination of L(L=M:K) code groups are selected.

This process gives the following result when the pre-selected secondarysynchronization codes SSC are given by discarding 4 secondarysynchronization codes SSC having the worst value of the off-peak maximumauto-correlation side-lobe values (MAS) or the worst value of the rootof the mean of the energy peaks (RMS) in the auto-correlation function{SSC₂, SSC₉, SSC₁₄; SSC₆, SSC₁₂, SSC₁₅; SSC₀, SSC₁, SSC₈; SSC₃, SSC₇,SSC₁₃}.

Another solution would be: {SSC₇, SSC₁₃, SSC₁₄; SSC₆, SSC₁₂, SSC₁₅;SSC₀, SSC₁, SSC₈; SSC₂, SSC₃, SSC₉}.

When the pre-selected secondary synchronization codes SSC are given bydiscarding 4 secondary synchronization codes SSC having the worstmaximum cross-correlation peak value (MCP) or the worst root of the meanof the energy peaks (RMS) in their cross-correlation function with theprimary synchronization code PSC: {SSC₄, SSC₆, SSC₁₀; SSC₁₂, SSC₁₃,SSC₁₄; SSC₀, SSC₁, SSC₁₅; SSC₅, SSC₈, SSC₁₁}.

INDUSTRIAL APPLICABILITY

As has been described, the method according to the invention forallocating secondary synchronization codes to a base station of a mobiletelecommunication system is very useful to a system for allocatingsecondary synchronization codes to a base station of a mobiletelecommunication system, which is mounted in various mobile terminalsof every kind of a mobile telecommunication system.

1. A method of communication between a base station and mobile stationsin a UMTS telecommunication system, comprising: transmitting to themobile stations a primary synchronization code as well as a sub-set ofsecondary synchronization codes belonging to 12 predetermined secondarysynchronization codes selected from 16 possible secondarysynchronization codes (SSC0, . . . , SSC15); and transmitting otherinformation to the mobile stations.
 2. The method of communicationaccording to claim 1, wherein the 12 predetermined secondarysynchronization codes are those having best values of an off-peakmaximum auto-correlation side-lobe value (MAS) in their auto-correlationfunction among the 16 possible secondary synchronization codes (SSC0, .. . , SSC15).
 3. The method of communication according to claim 1,wherein the 12 predetermined secondary synchronization codes are thosehaving best values of a root of a mean of energy peaks (RMS) in anauto-correlation function among the 16 possible secondarysynchronization codes (SSC0, . . . , SSC15).
 4. The method ofcommunication according to claim 1, wherein the 12 predeterminedsecondary synchronization codes are those having best maximumcross-correlation peak values (MCP) in a cross-correlation function witha primary synchronization code among the 16 possible secondarysynchronization codes (SSC0, . . . , SSC15).
 5. The method ofcommunication according to claim 1, wherein the 12 predeterminedsecondary synchronization codes are those having best values of a rootof a mean of energy peaks (RMS) in a cross-correlation function with aprimary synchronization code among the 16 possible secondarysynchronization codes (SSC0, . . . , SSC15).
 6. The method ofcommunication according to claim 1, wherein the 12 predeterminedsecondary synchronization codes having a best maximum cross-correlationpeak values (MCP) in their cross-correlation function with a remainderof the 16 possible secondary synchronization codes (SSC0, . . . ,SSC15).
 7. The method of communication according to claim 1, wherein the12 predetermined secondary synchronization codes having best values of aroot of a mean of energy peaks (RMS) in a cross-correlation functionwith a remainder of the 16 possible secondary synchronization codes(SSC0, . . . , SSC15).
 8. The method of communication according to anyone of claims 1 to 7, characterized in that the base station transmitsto the mobile stations a sub-set of 3 secondary synchronization codesamong the 12 predetermined secondary synchronization codes selected. 9.A telecommunication system, comprising: a base station; and a pluralityof mobile stations, wherein the base station is configured to transmitto the plurality of mobile stations a primary synchronization code aswell as a sub-set of secondary synchronization codes belonging to 12predetermined secondary synchronization codes selected from 16 possiblesecondary synchronization codes (SSC0, . . . , SSC15).
 10. A basestation for a UMTS telecommunication system comprising a base stationand mobile stations, comprising: a transmitting configured to transmitto the mobile stations a primary synchronization code as well as asub-set of secondary synchronization codes belonging to 12 predeterminedsecondary synchronization codes selected from 16 possible secondarysynchronization codes (SSC0, . . . , SSC15).
 11. A mobile station for aUMTS telecommunication system comprising a base station and mobilestations, comprising: a receiver configured to receive a sub-set ofsecondary synchronization codes belonging to 12 predetermined secondarysynchronization codes selected from 16 possible secondarysynchronization codes (SSC0, . . . , SSC15).
 12. A method for allocatingsecondary synchronization codes to a base station in a UMTStelecommunication system, comprising: allocating a sub-set of secondarysynchronization codes belonging to 12 predetermined secondarysynchronization codes selected from 16 possible secondarysynchronization codes (SSC0, . . . , SSC15); and using the allocatedsub-set of secondary synchronization codes in said base station tofacilitate communications to a plurality of mobile stations.
 13. Themethod for allocating secondary synchronization codes according to claim12, wherein the 12 predetermined secondary synchronization codes havingbest values of an off-peak maximum auto-correlation side-lobe value(MAS) in an auto-correlation function among the 16 possible secondarysynchronization codes (SSC0, . . . , SSC15).
 14. The method forallocating secondary synchronization codes according to claim 12,wherein the 12 predetermined secondary synchronization codes having bestvalues of a root of a mean of energy peaks (RMS) in an auto-correlationfunction among the 16 possible secondary synchronization codes (SSC0, .. . , SSC15).
 15. The method for allocating secondary synchronizationcodes according to claim 12, wherein the 12 predetermined secondarysynchronization codes having best maximum cross-correlation peak values(MCP) in a cross-correlation function with a primary synchronizationcode among the 16 possible secondary synchronization codes (SSC0, . . ., SSC15).
 16. The method for allocating secondary synchronization codesaccording to claim 12, wherein the 12 predetermined secondarysynchronization codes having best values of a root of a mean of energypeaks (RMS) value in a cross-correlation function with a primarysynchronization code among the 16 possible secondary synchronizationcodes (SSC0, . . . , SSC15).
 17. The method for allocating secondarysynchronization codes according to claim 12, wherein the 12predetermined secondary synchronization codes have a best maximumcross-correlation peak values (MCP) in their cross-correlation functionwith a remainder of the 16 possible secondary synchronization codes(SSC0, . . . , SSC15).
 18. The method for allocating secondarysynchronization codes according to claim 12, wherein the 12predetermined secondary synchronization codes having best values of aroot or a mean of energy peaks (RMS) in a cross-correlation functionwith a remainder of the 16 possible secondary synchronization codes(SSC0, . . . , SSC15).
 19. The method for allocating secondarysynchronization codes according to any one of claims 12 to 16,characterized in that the base station transmits to the mobile stationsa sub-set of 3 secondary synchronization codes among the 12predetermined secondary synchronization codes selected.
 20. Atelecommunication system, comprising: a base station; and mobilestations, wherein the mobile stations are configured to receive asub-set of secondary synchronization codes belonging to 12 predeterminedsecondary synchronization codes selected from 16 possible secondarysynchronization codes (SSC0, . . . , SSC15).
 21. A method ofcommunication between a base station and mobile stations in a UMTStelecommunication system, comprising: receiving by the mobile stations asub-set of secondary synchronization codes belonging to 12 predeterminedsecondary synchronization codes selected from 16 possible secondarysynchronization codes (SSC0, . . . , SSC15).
 22. A method ofcommunication between mobile stations and base stations in atelecommunication system, comprising: receiving secondarysynchronization codes (SSCs) from only one of five sets of twelvesynchronization codes comprising, {SSC0 SSC1, SSC2, SSC3, SSC6, SSC7,SSC8, SSC9, SSC12, SSC13, SSC14, SSC15}, {SSC0, SSC1, SSC3, SSC4, SSC5,SSC6, SSC8, SSC10, SSC12, SSC13, SSCT4, SSC15}, {SSC0, SSC1, SSC4, SSC5,SSC6, SSC5, SSC10, SSC11, SSC12, SSC13, SSC14, SSC15}, {SSC0, SSC1,SSC2, SSC4, SSC8, SSC9, SSC10, SSC11, SSC12, SSC13, SSC14, SSC15}, and{SSC0, SSC2, SSC4, SSC5, SSC6, SSC7, SSC8, SSC10, SSC11, SSC12, SSC13,SSC14}.
 23. A method of communication between a base station and mobilestations in a UMTS telecommunication system, comprising: transmitting tothe mobile stations a primary synchronization code as well as a sub-setof secondary synchronization codes belonging to 12 predeterminedsecondary synchronization codes selected from 16 possible secondarysynchronization codes (SSC0, . . . , SSC15); transmitting otherinformation to the mobile stations; and receiving the transmittedprimary synchronization code and the sub-set of secondarysynchronization codes for synchronization between the base station andthe mobile stations.